The preparation of functionalized substrates is an area of interest for many commercial applications ranging from biosensors to energy conversion devices. Biosensors are designed to determine the presence of biomolecules and are often used in biotechnology industries to perform rapid biochemical analysis. These biosensors are adapted to detect and/or quantify various analytes based on known interactions between the analytes and other biomolecules immobilized on a substrate, such as glass. Organosilane chemistry is a typical method used to attach biomolecules to glass. Unfortunately, these and other methods used to immobilize biomolecules on glass substrates suffer from irreproducibility and instability, resulting in increased manufacturing costs and short shelf life.
Oxide materials, especially TiO2, are often used in energy conversion devices. The bonding of molecules such as dye molecules to the surface of TiO2 provides a way to modify the optical properties and enhance the performance of some energy conversion devices, such as dye-sensitized solar cells. These surface molecular layers play an important role in controlling the electrical properties of TiO2 and other oxide materials. These layers are able to modify the density of mid-gap surface states, alter the charge transfer from dye molecules to TiO2, and control the degree to which redox-active species such as I−I3− can undergo direct recombination processes at the surface. Conventional schemes for functionalizing TiO2 use organic molecules having functional groups such as phosphonic acid, carboxylic acid, ester, acid chloride, carboxylate salt, amide, silane, ether, acetylacetonate, and salicylate. See Galoppini, E., Coordination Chemistry Reviews, 248 (2004) 1283-1297. In the case of silanes and ethers, the functionalization involves reaction of these functional groups with surface titanol (Ti—OH) groups and, thus, depends on the amount of surface titanol groups. Previous work using ester linkages has shown that there are multiple bonding sites depending on the pH and degree of hydration of the surface. See Finnie, K. S. et al., Langmuir 1998, 14, 2744; and Vittadini, A. et al., J. Phys. Chem. B 2005, 109, 20938. A problem with these conventional schemes is that the synthetic methods are complex, costly, and time consuming. In addition, many of the resulting linkages to the metal oxides are weak and unstable.